Forwarder: clear buffers on connection lost

Unfinished transfers would remain in buffers when we lost connection.

In case of TCP, this is a problem. A message might be half-way send when
the connection drops, resulting in the other half being sent after the
TCP connection reestabilishes. The collector would interpret this as an
entirely new message, resulting in bogus data being decoded.

Author: sedmicha

src/plugins/output/forwarder/src/Connection.cpp

@@ -87,8 +87,7 @@ Connection::forward_message(ipx_msg_ipfix_t *msg)
         sender.process_message(msg);
 
     } catch (const ConnectionError &err) {
-        // In case connection was lost, we have to resend templates when it reconnects
-        sender.clear_templates();
+        on_connection_lost();
         throw err;
     }
 }
@@ -107,31 +106,36 @@ Connection::advance_transfers()
 
     IPX_CTX_DEBUG(m_log_ctx, "Waiting transfers on connection %s: %zu", m_ident.c_str(), m_transfers.size());
 
-    for (auto it = m_transfers.begin(); it != m_transfers.end(); ) {
+    try {
+        for (auto it = m_transfers.begin(); it != m_transfers.end(); ) {
 
-        Transfer &transfer = *it;
+            Transfer &transfer = *it;
 
-        assert(transfer.data.size() <= UINT16_MAX); // The transfer consists of one IPFIX message which cannot be larger
+            assert(transfer.data.size() <= UINT16_MAX); // The transfer consists of one IPFIX message which cannot be larger
 
-        ssize_t ret = send(m_sockfd.get(), &transfer.data[transfer.offset],
-                           transfer.data.size() - transfer.offset, MSG_DONTWAIT | MSG_NOSIGNAL);
+            ssize_t ret = send(m_sockfd.get(), &transfer.data[transfer.offset],
+                               transfer.data.size() - transfer.offset, MSG_DONTWAIT | MSG_NOSIGNAL);
 
-        check_socket_error(ret);
+            check_socket_error(ret);
 
-        size_t sent = std::max<ssize_t>(0, ret);
-        IPX_CTX_DEBUG(m_log_ctx, "Sent %zu/%zu B to %s", sent, transfer.data.size(), m_ident.c_str());
+            size_t sent = std::max<ssize_t>(0, ret);
+            IPX_CTX_DEBUG(m_log_ctx, "Sent %zu/%zu B to %s", sent, transfer.data.size(), m_ident.c_str());
 
-        // Is the transfer done?
-        if (transfer.offset + sent == transfer.data.size()) {
-            it = m_transfers.erase(it);
-            // Remove the transfer and continue with the next one
+            // Is the transfer done?
+            if (transfer.offset + sent == transfer.data.size()) {
+                it = m_transfers.erase(it);
+                // Remove the transfer and continue with the next one
 
-        } else {
-            transfer.offset += sent;
+            } else {
+                transfer.offset += sent;
 
-            // Finish, cannot advance next transfer before the one before it is fully sent
-            break;
+                // Finish, cannot advance next transfer before the one before it is fully sent
+                break;
+            }
         }
+    } catch (ConnectionError& err) {
+        on_connection_lost();
+        throw err;
     }
 }
 
@@ -261,3 +265,16 @@ Connection::check_socket_error(ssize_t sock_ret)
         throw ConnectionError(errbuf);
     }
 }
+
+void
+Connection::on_connection_lost()
+{
+    for (auto& p : m_senders) {
+        // In case connection was lost, we have to resend templates when it reconnects
+        Sender& sender = *p.second.get();
+        sender.clear_templates();
+    }
+
+    // Do not continue any of the transfers that haven't been finished so we don't end up in the middle of a message
+    m_transfers.clear();
+}

src/plugins/output/forwarder/src/Connection.h

@@ -181,4 +181,7 @@ class Connection {
 
     void
     check_socket_error(ssize_t sock_ret);
-};
+
+    void
+    on_connection_lost();
+};